im not sure if the frog is actually too worried about getting some uv rays. but i wouldnt put a heat lamp on plexi glass just because it might warp/melt it. ive never had plexi glass so i wouldnt know. i would only put a lamp on the screen. if you need to cool your tank down just dont use a light. the only light i have hooked up is a compact fllourescent bulb. it doesnt change the temperature of my tank at all. maybe 1 degree max. and i use it for a day light. once it starts getting dark outside i switch it off.